How to batch shrink images for the web using ImageMagick
This command works well to shrink 6MB JPGs from my DSLR to a more manageable 300kB. You may need to adjust your -resize command. Check out the reference links for details (especially on the gaussian-blur).
mogrify -strip -interlace Plane -gaussian-blur 0.05 -quality 85% -resize 2144x1424 -path ./sm *.JPG